In a small bowl, combine the first eight ingredients until smooth; set aside. In a large skillet or wok, stir-fry beef in 3 tablespoons oil until meat is no longer pink. Remove and keep warm. In the same skillet, stir-fry cauliflower and carrots in remaining oil for 5 minutes. Add broccoli; stir-fry for 7 minutes. Add mushrooms; stir-fry 6-8 minutes longer or until the vegetables are crisp-tender.

Stir broth mixture and add to the pan. Bring to a boil; cook and stir for 2 minutes or until thickened. Reduce heat; add beef and peanut butter. Cook and stir over medium heat until peanut butter is blended. Serve with spaghetti. Sprinkle with peanuts. Makes 6 servings.